CBQE-0: fix upgradeXDCR hangs

Change-Id: Ib60044f45ea5f24c788956d8194d269eec40df54
Reviewed-on: http://review.couchbase.org/26409
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Andrei Baranouski <andrei.baranouski@gmail.com>